Evolutionary studies on optimal decisions or conservation guidelines are often derived by generalising patterns from a single population, while inter-population variability in life-history traits is seldom considered. We investigated here how survival and recruitment probabilities changed with age at different geographical scales using the encounter histories of 5523 European storm petrels from three Mediterranean colonies, and also how our estimates of these parameters might be expected to affect population growth rates using population matrix models. We recorded similar patterns among colonies, but also important biological differences. Local survival, recruitment and breeding success increased with age at all colonies; the most distant of three colonies (Marettimo Is.) showed the largest differences. Strikingly, differences in recruitment were also found between two adjacent colonies (two caves from Benidorm Is.). Birds marked as adults from Marettimo and Benidorm colonies had a different survival, whereas we found no differences within Benidorm. Differences in survival were no longer apparent between the two islands at the end of the study following a reduction in predation by specialist gulls at Benidorm. Since birds marked as fledglings mostly recruited near the end of the study, their overall survival was high and in turn similar among colonies. Results from our population matrix models suggested that different age-dependent patterns of demographic parameters can lead to similar population growth rates. Variability appeared to be greater for recruitment and the most sensitive parameter was adult survival. Thus conservation actions targeting this vulnerable species should focus on factors influencing adult survival. Differences in survival and recruitment among colonies could reflect the spatial heterogeneity in mortality due to predation and colony-specific density dependent processes. Results highlight the importance of taking into account the potential spatio-temporal heterogeneity among populations in vital rates, even in those traits that life-history theory considers less important in driving population dynamics.

Capture-mark-recapture methods are used widely for monitoring and diagnosis of bird populations as they permit robust estimates of population abundance and demographic parameters (e.g. survival) to be obtained from incomplete records of individual life histories. The statistical analysis of these data relies on the important assumption that individuals of the same local populations (i.e. colony) have the same parameters (the homogeneity assumption). We used data from six medium-to long-term monitoring schemes of local Mediterranean populations of the European Storm Petrel Hydrobates pelagicus to empirically show that the level of individual heterogeneity and the consequent bias in the parameter of interest depend on the recapture methodology, which has important consequences for the experimental design. We found that the recapture probability varied over time and among methodologies. The study design had a strong influence on the proportion of transients caught (i.e. individuals not recaptured after marking); however, the survival probability estimate for resident birds was fairly similar across the studies. The differences found in survival seem to depend on the biological variability between sites (e.g. predation pressure), and not on the recapture methods.

The breeding performance and foraging of blue and great tits, and the abundance of arthropods living on the trees of an oakwood and of a coniferous reafforestation were studied in Sicily, in order to: 1) compare breeding parameters in natural and seminatural habitats within the same area; 2) estimate the degree of overlap in peak resource and peak demand of young tits, and the overlap of nestling diet of the two species in the two habitats. Both species had earlier laying dates, laid more eggs and raised more fledglings in the oakwood than in the reafforestation; they achieved the same fledging success within the same habitat type. These differences are probably due to the earlier and higher food peak in oak compared to pine. Food brought to the nestlings differed between habitats and between species: blue tits always brought small prey from a limited number of taxa, while great tits changed both prey taxa and size depending on habitat. The more flexible food of the great tit is in line with the smaller reduction in number of fledglings in pine reafforestation compared to oakwood. It is suggested that tits have developed a mechanism to lay eggs at different dates in accordance with the habitat resource where adults catch prey for nestlings. Finally, mean clutch sizes of blue tits between habitats were well correlated, but the process seemed different in the great tit. Significant correlation was indeed detected between the proportion of great tits breeding in oakwood and the difference in the clutch size between the habitats. This suggests that more great tits settled in oakwood in years when conditions were more suitable to produce bigger clutches.

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